Captain (Military Officer)
Barnacles
Barnacles is the brave polar bear captain of the Octonauts. He can drive any ship or gup, and is strong enough to lift a giant clam. Catchphrases: "Octonauts, let's do this", "Sound the Octo-Alert!", "Octonauts, to the launch bay!" and "Hold on, this could get bumpy".

Lieutenant and Cryptozoologist (Sailor, Steam)
Kwazii
A cat who speaks in a Cockney accent. Kwazii is a daredevil cat with a mysterious pirate past. He believes in many sea monsters such as the Nackerwhack, Tri-Toothed-Terror, Giant Shrimp Monster, Monster of Creepy Cove and others and likes to drive fast in the Gup-B. In the episode "The Octonauts and the Giant Spider Crab", it is revealed that he has a fear of spiders. Catchphrases: "Shiver me whiskers" and "Yeow!".

Medic (Doctor)
Peso Penguin
He is a penguin with a British accent (Spanish accent in the US version) and the medic of the Octonauts. He is not fond of scary situations, but if someone is hurt or in trouble he can be the bravest Octonaut of all. He has a younger brother called Pinto. Catchphrase: "Flappity flippers!".

Oceanographer and Founder (Aristocrat or Scientist)
Professor Inkling, Inkling, or Professor
An octopus who speaks in a posh accent. Inkling brought the Octonauts together, to study the oceans and have adventures. Catchphrase: "Fascinating!"

Scientist (Marine biologist) (Scientist)
Shellington (Dr)
A sea otter who speaks with a Scottish accent. Shellington is a scientist who knows a lot about ocean creatures. He is not a very good driver and once crashed the GUP-D. Catchphrase: "Jumping jellyfish!" and "Fascinating".

Engineer (Brassman)
Tweak
A rabbit who speaks with a Southern-US accent. Tweak lives and works in the launch bay. She often invents things like the GUP-X, GUP-S, the Octo-Max suit, and the Friend Finder she made for her friend, Sandy the leatherback sea turtle. She often refers to Captain Barnacles as "Cap". Catchphrases: "Right away, Cap!" and "...faster than you can say 'buncha munchy crunchy carrots'!".

Information technology Officer and Photographer (Journalist)
Dashi
A dog who speaks with a New Zealand accent (American in the US version). Dashi is the photographer for the Octonauts, and takes care of all the computers aboard the Octopod. Catchphrase: "Already on it captain!".

Ship's Cook and Gardener
Tunip
Vegimals are half-animal, half-vegetable creatures – Tunip is half-tuna, half-turnip. He loves to make kelp cakes and work in the garden-pod. He often faints at shocking news. Catchphrase: "Cheepa cheepa!" and "Zuupa zuupa!". He and the other vegimals primarily speak Vegimalese, a language made of chirps and warbles that only Shellington understands (sometimes), though they also speak a limited amount of English (with a Vegimalese accent). The vegimals were discovered by Shellington as eggs attached to the side of the Octopod. To protect them he brought them into his lab, where they hatched a few days later. After a few weeks they established themselves as an integral part of the crew.[11]